Loud speaker



NOV. 8,1932. E, s, PRlDHAM 1,885,735

LOUD SPEAKER Filed Feb. 19, 1929 2 Sheets-Sheet 1 INVENTOR.

ATTORNEYS.

Nov. 8, 1932. I E. s. PRlDHAM 1,886,735

LOUD SPEAKER Filed Feb. 19, 1929 2 Sheets-Sheet 2 JN V EN TOR. 6W 7 mm A TTORNEYS.

(9M1, film Patented Nov. 8, 1932 armer rates EDWIN S. PRIDI-IAM, OF OAKLAND, CALIFORNIA, ASSIGNOB TO THE IVIAGNAVOX GOM PANY, OF OAKLAND, CALIFORNIA, A CORPORATION OF ARIZONA LOUD SPEAKER Application filed February 19, 1929. Serial No. 341,231.

ing afield magnet and enclosed in a housing which forms a magnetic path leading across a narrow air gap in which a moving 0011 18 disposed. It is essential that the moving coil be exactly centered in the air gap and that the elements of the magnetic structure forming the air gap be also exactly centered. This moving coil, in present-day practice, is mounted directly on the apex of a conical diaphragm flexibly supported at its rim by a frame which is secured to a portion of the magnet housing. Should this diaphragm, which is usually of paper, be punctured, it is advantageous to be able to substitute another 1- diaphragm assembly without resorting to factory methods and fixtures for exactly centering the coilin the narrow air gap. In other words, it is highly desirable that a structure be'provided in which interchangeability of Jarts is Jermitted so that the dia lira 'm assembly of one device will fit the magnetic structure of any other device.

In addition, it has become general in the trade for a manufacturer of radio receiving sets to obtain loud speakers from some distant source, and one of the largest items of cost in the shipping of these loud speakers is the field coil or winding, which of itself weighs almost as much as the remainder of the structure. In and by the present invention, a structure is provided in which all of the elements except the field coil or winding may be shipped to the manufacturer of the receiving set, and the latter without any difficulty or without special tools or equipment, may insert the field coil and be assured that the parts when assembled will be correctly spaced and centered. Such a structure requires ready accessibility to the interior of the housing, so as to permit of insertion of the field coil, which usually requires demounting, and facility of reassembly without special tools or equipment in the way of centering devices.

In the accompanying drawings,

Fig. 1 shows a longitudinal central sectional view of one form which my/invention may assume;

Fig. 2 shows a plan view in section of j the same, taken on the line II-II of Fig. 1;

Fig. .8 shows a longitudinal centralsectional view of a slightly modified form of the invention, in which the top portion of the housing is removable; r Fig. 4 shows a similar view of a further modification, in which the bottom plate of the housing is removable. 1 I

Fig. 5 a view in elevation showing the spacing ring used for centering andproperly locating the poles of themagnetic structure. The device as herein shown-comprises an iron housing 10, usually cylindrical in form,

and containing an axial field magnet 11 and a field coil 12. The field magnet is secured to one end of the housing and projects through an opening in the opposite end of the housing, which openingis slightly larger than'the field magnet, so as to leave a very narrow,

circular air gap. The housing, for the sake of accessibility, may be partednear its middle portion as shown in Fig. 1, the two halves beflanges 14; oras shown in Figs. 3 and; 4,"one of the end walls, either the top or bottom, may be separately formed and detachably secured to the remainder of the housing by suitable fasteners 15. I

' Thefield coil 12 is removablymounted in the housing,'fitting freely around the; field magnet 11 and being held in place by means of a nut 16 on the field magnet, as shown in Fig. 1; or by other means, such as wedges 17 or other like fasteners between the coil and housing, as shown in Figs. 3 andl; Secured to one end wall of the housing is a diaphragm-holding frame 18 carrying a diaphragm 19 preferably in the form of a cone, on the apex of which is mounted a movable coil 20. It is essential that this coil be exactly centered within the annular air gap, andthat the said gap be perfectly true. In order to insure centering of the elements forming the air gap, and a correct positioning of the coil therein, without the use of special tools when assembling the separable parts of the housing, one of which in all cases carries the ing secured together by bolts 13 fastened'in diaphragm assembly, includingthe movable coil, and the other of which carries the field magnet 11, I provide a spacing ring 21 on the inner side of the apertured end wall of the magnet housing, which spacing ring is of brass or other non-magnetic material, and is formed with an opening of the exact size of the adjacent end of the field magnet 11, over which it fits snugly. This spacing ring is riveted or otherwisesecured in place on said end wall with the aid of a fixture which insures that when it is finally placed over the end of the field magnet 11 the projecting end of the latter will be exactly centered with respect to the opening in the adjacent end wall of the magnet housing, leaving an air gap of even spacing throughout.

The rim of the conical diaphragm should be supported and restrained against blasting; and this is preferably accomplished by the use of a connecting strip or band 19 of limp leather or the like, between the rim of the cone and the supporting frame 18. The use of such connecting bands permits of a certain freedom of movement laterally of the apex of the cone and the vibrating coil carried thereby, to such an extent that additional and adjustable spacing means are required, to insure exact centering of the vibrating coil.

The moving coil and the apex of the cone must be flexibly supported so as to permit free movement of both in an axial line while restraining them against any lateral movement. .This may be done in several ways, one

such consisting of a plurality of extremely thin arms 22, of light material, having a certain degree of resilience or spring'iness secured at their inner ends to theframe of the moving coil, and at their outer ends to a ring. 23. This ring 23 is held in place on the outer surface of the end wall of the housing in which the air gap is formed, by means of screws 24 passing through the spacing rings -21 and thence through large openings in said endwall. lVhen the screws are loosened, the ring 23 may be shifted about sufficiently, on account of the large openings, to bring the moving coil'20 into the exactposition it should occupy in the air gap; whereupon, by. tightening the screws, the position of the coil becomes fixed. This operation is done. in

the factory, and a convenient way of carrying it out is to place the diaphragm assembly in inverted position, with-a fixture corresponding: in sizevto the'end of the'field magnet 11 passing through the opening in the spacing .ring 2122L1'ld into the interior of the movable coil. The said spacing ring is notched out in-several places as indicated at 25, so that ethe operator may be able to see when the coil is in correct position. The screws 24 are then tightened up, and this setting, having once been made, should remain unchanged.

As a result of'this construction, the diaphragm assembly can easily and quicklybe otherwise securing the two elements of the housing together. Even though the parts fit loosely, or their former position is slightly disturbed, the setting of the air gap and the position of the moving coil therein will always be correct, owing to the spacing ring 21. As above stated, this is of great advantage in that it permits shipping of the device without the field coil, the latter being inserted at a later time when ready for'final assembly; and it also permits of repairs'being made involving the replacement oi the diaphragm or moving coil. When this occurs, the diaphragm assembly is simply removed and another assembly of the same size substituted, the spacing ring again insuring that the parts will be correctly fitted together and the mov ing coil accurately spaced.

Having thus described my invention, what I claim new and desire to secure by Letters Patent is:

1. A method of constructing. and assembling a loud speaker of the type employing a casing of magnetizable material,"formed' in .endwise, separablesections, with an aperture in one end and a fieldmagnet secured to the opposite end, the said field magnet extending through the aperture and spaced therefrom, so as to leave a narrow air gap in which is disposed a movable coil attached to a sound regenerating diaphragm, which consists of placing a spacing ring of non-magnetic material upon the apertured end wall having an opening of a size to exactly 'fit OVtfil'tilGdtljtCQIlt end of the field magnet, and so positioned as to bring the magnetic elements into position where the air gap is of uniform width throughout, and attaching through peripheral supporting means on the diaphragm, the said diaphragm and moving coil to the apertured end wall and centering the said moving coil with relation tothe aperture in the spacing ring by employment of shiftable, lockable connections between the said movin coil and the apertured end wall, and providing said spacing ring with a plurality of notches to reveal theposition of the moving coil relative to the aperture in the end wall, and a fixture inserted in the opening in the spacing ring. Y

2. A loudspeaker comprising a casingof ma gnetizable materiahformed with an opening in one end wall, a field magnet, within the casing, fixed to the opposite end wall and projecting into said opening'so as to" leave an annular air, gap, said casing being formed with endwise sections detachably connected together, a field coil in the casing surrounding said field magnet, a movable coil disposed in the said air gap, a conical diaphragm secured to said coil, a flexible support for the rim of the diaphragm, secured to the adjacent end wall of the casing, a spacing ring on the apertured end wall having an opening to exactly fit the adjacent end of the field magnet and bring thetwo parts of the easing into position where the air gap will be of uniform width throughout, and a flexible support for the movable coil adjustably secured upon the adjacent end wall of the casing-independent of said flexible support for the rim of the diaphragm, whereby the movable coil can be adjusted in the air gap independently of the diaphragmsupport.

3. A loud speaker comprising a casing of magnetizable material, formed with an open- Ing in one end wall, a field magnet within the casing, fixed to the opposite end wall and projecting into said opening so as to leave an annular air gap, said casing being formed with endwise sections detachably connected together, a field coil in the casing surrounding said field magnet, a movable coil disposed in the said air gap, a diaphragm secured to said coil, a support for the ri: of the diaphragm, secured to the adjacent end wall of the casing,'a spacing ring on the apertured end wall having an opening to exactly fit the adjacent end of the field magnet and bring the two parts of the casing into position where the air gap will be of uniform width throughout, and a shiftable locking connection between the moving coil and the apertured end wall for centering the said coil with relation to the opening in the spacing ring, said spacing ring being pro vided with a plurality of notches so positioned as to disclose the posit-ion of the movable coil relative to the apertured end wall when viewed from within the casing.

4. A loud speaker comprising a casing composed of magnetizable material, havin an opening in one end wall, a field magnet 'ithin the casing fixed to the opposite end wall and projecting into said opening so as to leave an annular air gap, said casing e ing formed in endwise, separable sections, and detachably connected together, a field coil removably received in said casing and loosely surrounding the said field magnet, a movable coil disposed in said air gap, a sound-regenerating diaphragm secured. to said movable coil, a support for the rim of said diaphragm, secured to the adjacent end wall of the casing, a spacing ring on the apertured end wall of the casing, having an opening to exactly fit the adjacent end of the field magnet and bring the two parts of the easing into position Where the air gap is of uniform width throughout, and a unitar shiftable, flexible connection between the movable coil and the aperturcd end wall,

for centering the said coil with relation to the spacing. ring, whereby the coil can be secured to and centered upon saidend Wall independently of said support for the rimof the diaphragm. I

5. A loud speaker comprising a casing formed ofmagnetizable material having an opening in one end wall, afield magnet within the casing fixed to the opposite end wall and projecting into, said opening so as to leave an annular air gap, said casing being formed in endwise, separable sections, detachably connected. together, a field coilin the c: sing surrounding said field magnet, a movable coildisposed in the air gap, a conical diaphragm secured. to said coil, a flexible support for the rim of the diaphragm, a second fiex'ble support for retaining the movable coil in a central position with respect to said airgap, and a plate like mounting for said second flexible support movably mounted. upon the outer surface of. said first end Wall independent of the flexible support for the. rim of the diaphragm to facilitate a centering. of the movablecoil to which the diaphragm is attached without moving the diaphragm support.

6. In a Ploud speaker of the moving coil type the combination ofra frame structure having oppositely disposed end portions between which an energizing coil is mounted, a magnetic core for said coil secured to one of. said endportions and projected through an opening'in the opposite end portion, said opening in said latter end portion being larger than the projecting end ofsaid core. to provide an. annular airv gap, a diaphragm support mountedupon said latter end portion, a: conical diaphragm having its periphery secured against radial movement upon said diaphragm support, a diaphragm actuat ing coil upon said diaphragm disposed around the end of said core and in said air gap, an axially flexible support for'said coil, and means upon which said flexible support is mounted, adjustably securedto the adjacent end portion, whereby the diaphragm actuating coil and said flexible support may be adjusted upon saiddatter end. portion to lo cate the diaphragm actuating coil-concentric in the air gap without displacing the diaphragm on its support.

7. Ina loud speaker of themoving coil type the combination of a magnetic field frame member having an axially extending portionupon which there is formed an open end portioniwith an outwardly extending flange and a. closed end portion in which there is formed an opening, a second frame portion secured to the outwardly extending flange of said first portion, anda core secured uponisaid second frame: portion adapted to project into the opening in said first port-ion to forman-annular airlgap. i s

8. The method of mounting and centering ently adjusted and centered'in proper rela- I tion in the air gap without disturbing the diaphragm support.

' 9. In a loud speaker of the electro-dynamic type, the combination of a magnetic frame structure having an inner pole and an outer annular pole between which an annular air gap is formed, a diaphragm having an actuating coil adapted to be disposed in said air gap, a supporting means for the periphery of said diaphragm mounted upon and carried by said annular pole piece, and adjustable plate secured upon said annular pole piece independently of said supporting means, and a flexible centering device attached to the diaphragm adjacent its actuating coil and secured to said plate, said plate being adjustable upon said annular pole piece independently of the supporting means for the pe riphery of the diaphragm so that the coil can be centered within the gap independently of the diaphragm support.

10. In a loud speaker of the electro-dynamic type, the combination of a magnetic frame structure having an inner pole and J an outer annular pole between which an annular air gap is formed, a diaphragm having an actuating coil adapted to be disposed in said air gap, a supporting. means for the periphery of said diaphragm fixed upon said annular pole piece,.an adjustable plate having an outwardly projecting surface secured upon said annular pole piece independently of said supporting means, and a flexible centering device attached to the diaphragm adja'cent its actuating coil and secured to the outwardly projecting surface upon said plate, said plate and flexible centering device eing adjustable upon said annular pole piece independently of the support for the periphery of the diaphragm so that the coil can be centered within the gap independently of the diaphragm support.

11. In a loud speaker of the electro-dyna-mic type, the combination of a conical dia- I phragm having an actuating coil secured thereto, an" inner pole piece, an outer pole piece disposedabout the end of said inner pole piece and forming an annular air gap or the actuating coil upon said diaphragm, a supporting means secured upon said annular pole piece projecting outwardly thereflexible member extending from said diaphragm and secured to said plate.

12. In a loud speaker of the electro-dynamic type, the combination of a conical diaphragm having an actuating coil secured thereto, an inner pole piece, an outer pole piece disposed about said inner pole piece to form an annular air gap for the actuating coil upon said diaphragm, a supporting means secured upon said annular pole piece ,1; pro ecting outwardly therefrom upon which plate.

EDIVIN S. PRIDHAM.

from upon' which the periphery of said diaphragm is secured, a second support for said diaphragm comprising a plate adjustably secured upon said annular pole piece independently of said first support, and: a one piece 

